1. Field of the Invention
The present invention relates to cleaning a plate-like electrode having serrated edges (hereinafter referred to as "plate electrode") for use in a charging device for image forming apparatus such as copiers, printers and the like.
2. Description of the Related Art
In conventional image forming apparatus such as copiers, printers and the like, charging devices are used to charge an image-carrying member, transfer a toner image from said image-carrying member onto a transfer sheet, and separate said transfer sheet from said image-carrying member. A linear type electrode comprising a wire of about 50 .mu.m to accomplish discharge is typically used as the aforesaid charging device.
Charging devices of the aforesaid type, however, are disadvantageous inasmuch as the extremely fine wire used as the aforesaid linear electrode is readily broken, thereby making it very difficult to assemble the charging device.
When a charging device using the aforesaid linear electrode emits a discharge to an image-carrying member, said discharge rises 360.degree. around the wire used as the electrode, such that the majority of the discharge current does not flow to the image-carrying member side, but flows to a stabilizer or the like provided around the periphery of said wire. Furthermore, the percentage of the discharge current that flows to the image-carrying member is small, making it necessary to supply a large current to achieve adequate discharge relative to the image-carrying member, thus a high voltage current is applied to said wire.
However, it is extremely dangerous to handle said wire when a high voltage is applied to the wire as previously described. Furthermore, a large amount of ozone is generated by the aforesaid discharge, such that the ozone thus generated causes deterioration of the cleaning blade and image-carrying member and the like, as well as adversely affecting the environment.
The use of plate electrodes as corona charging devices that generate small amounts of ozone is well known. A plate electrode is disclosed in Japanese Laid-Open Patent Application No. Hei 1-312563, wherein said electrode is provided with a plate projection. When using a plate electrode, only 1/4 the amount of ozone is generated compared with the amount of ozone generated when using a corona wire under identical output. When a plate electrode is used, the discharge current may be reduced because a large current flow to the stabilizer is not necessary to stabilize the discharge. Thus, if the discharge current is reduced, the amount of ozone generated can also be reduced.
In corona charging devices using a plate electrode, silicon (Si) adheres to and grows radially on the exterior periphery of the plate electrode due to repeated discharges, and said silicon growth causes irregular discharges. Over time, toner and paper debris adhere to the plate electrode and cause irregular discharges. When a corona charging device which is in a state of generating irregular discharges is used for discharge, while streaks are produced in the formed image, and produce locally inadequate transfer when used to effect transfers.
Silicon that adheres to the plate electrode can be removed by light rubbing, and if removed, discharge is stabilized. Cleaning devices for removing silicon and the like adhering to a plate electrode are well known, such as that disclosed in Japanese Laid-Open Utility Model Application No. Hei 2-75658. This cleaning device rotates while pressing a roller-shaped sponge member against plate electrode from the direction of discharge. The plate electrode is embedded in the aforesaid sponge member via the pressure applied by said sponge member, such that the silicon adhered to the lateral surfaces of the plate electrode is removed therefrom.
In the cleaning device disclosed in the previously mentioned Japanese Laid-Open Utility Model Application No. Hei 2-75658, the tip of the plate electrode become caught in the fine holes in the surface of the sponge member so as to damage said sponge member, and the sponge fragments torn from the sponge member during said contact adhere to the tip of the electrode causing irregular discharge. Because the sponge member presses from the direction of discharge, the tip of the plate electrode may become bent.